Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a first image in a sequence for a display screen or portion thereof with transitional graphical user interface, showing our new design;

FIG. 2 is a second image in a sequence thereof; and,

FIG. 3 is a third image in a sequence thereof.

The broken lines illustrating portions of the transitional graphical user interface form no part of the claimed design.

The outermost broken lines illustrating the display screen or portion thereof form no part of the claimed design.

The appearance of the image transitions sequentially between the images shown in FIGS. 1-3. The process or period in which one image transitions to another forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 